Textile substrates need various chemical treatments depending on the desired properties for the substrates in their end-use applications. Wet chemical treatment for textile substrates can be performed either by batch or continuous process. For a typical batch process, a specific amount of textile substrate is treated with chemical formulations for a specific period of time. The amount of chemicals used is normally based on the amount of the substrate being treated. For continuous textile wet processes, textile substrates are treated continuously by being passed through one or more process steps arranged in tandem. Textile substrates pass through a chemical formulation in a treatment bath, and then the completely soaked substrates pass through a pair of squeeze rollers to remove excess amounts of the chemical formulation in order to control the amount of chemical formulation on the substrates. Then, in many continuous processes, the substrates continue to pass through a drying (e.g., heating) stage, such as an oven, to remove water and to fix the chemicals on the substrates. The amount of chemicals applied on textile substrates depends on the concentration of chemicals in the formulation and the “wet pickup”. Wet pickup is the amount of the chemical formulation picked up by the substrate and is expressed as a percentage of the weight of the dry substrate. The wet pickup on the substrate is controlled by the nip pressure of the squeeze rollers. To give uniform chemical distribution throughout or over the substrate, the wet pickup must be controlled evenly across the width and along the length of the substrate.
Many textile processes employ chemical treatments of textile substrates performed at the “fabric stage” (e.g., woven or knitted fabric). However, chemical treatments are also performed at the “fiber stage” (e.g., when chemical-treated fibers are required for yarn spinning or nonwoven production). For a batch process chemical treatment of fibers, a specified amount of loose fibers is loaded in a perforated basket, and the basket is loaded into chemical treatment equipment such as a stock dyeing machine. After loading the basket, a specific amount of chemicals is applied on the fibers using the dyeing machine. In contrast, in a continuous process, the fibers in a web or batt form are continuously passed through one or more process steps arranged in tandem. In operation, the fiber batt (or web) impregnated with a chemical formulation is passed through a pair of squeeze rollers. The amount of the chemical formulation picked up by the fibers is controlled by the pressure of the squeeze rollers. The wet pickup control for the fibers is difficult in a continuous process when compared to woven fabrics because the thickness of the fiber batt (or web) is generally uneven across the width and along the length.
If, in a continuous process, the fibers were subjected to scouring, bleaching, and rinsing, the fibers will likely contain only water after a final squeezing operation. In this case, even though there may be a variation of wet pickup on the fibers, this will generally not pose a problem since there will be no remaining chemical on the fibers after drying. In sharp contrast, when the fibers are subjected to chemical formulation treatment, the wet pickup variation will cause uneven chemical distribution throughout the final dried fibers. This will cause an uneven quality (property) on the final products (yarn or nonwoven) made with these fibers.
U.S. Pat. Nos. 4,213,218 and 4,944,070, each of which are herein incorporated by reference, describe methods of continuous wet finishing for fibers. These patents describe processes which require the loose fibers to be converted into a web or batt form before the wet treatment.
U.S. Pat. No. 4,213,218 describes a continuous chemical treatment of fiber batt. The fiber batt is impregnated with liquid (chemical) by repeated gentle squeezings while passing through the impregnation tank. When the batt leaves the tank, the batt passes through a pair of high-expression nip rolls which remove most of the fluid from the batt to get the target wet pickup. But it is difficult to handle loose fiber batt in the continuous wet process due to the low integrity between fibers in the batt. Especially when the wet fiber batt passes through the nip of a pair of squeeze rollers, there is a high possibility of batt deformation (breakage), which will cause uneven chemical distribution on the fibers as well as disruption of the continuous process.
U.S. Pat. No. 4,944,070 describes wet finishing of cotton fibers at increased speed. To do this, the cotton fibers are converted into an integral batt which has sufficient integrity to withstand the wet processing. This process requires additional equipment to provide integrity on the fiber batt and fully break the integrity after the wet process.